Appropriate visual presentation of measured data is essential in a variety of technological fields, for example, in medical and scientific research as well as in clinical practice. The visualization of volumetric data as a 2D image is achieved by visualization applications, for example, by a volumetric rendering application. The visualization application can be interactive, i.e., allow a user to control viewing parameters like the viewing angle and the magnification. Moreover, the visualization application can be remotely controlled. For example, the bulk of a rendering calculation can be executed on a specially equipped rendering computer, while the user controls the visualization from a different computer. Generally, the quality of the analysis and interpretation of the data depends on how efficient and with what quality such visualization applications can provide required image information to a user.
Medical applications handle, for example, volumetric data gained by computer tomography, radiography, cardiac or peripheral angiography, and nuclear magnetic resonance imaging. in such applications, medical personnel interact with the visualization applications to find the best view(s) of an object for the analysis. During such interactions, rendering algorithms calculate the different views. Typical rendering algorithms include ray casting and ray tracing algorithms.
In visualization applications, a rendered image is mainly a projection of a 3D volumetric object on a viewing (or imaging) plane. The projection can be either orthographic, paraperspective or perspective. A rendering algorithm can run, for example, on a single workstation or within a remote client-server system or a peer-to-peer system. Important requirements for a rendering system are high reliability of a fast, high quality visualization that allows as close as possible real time visualization of 3D data.
In a client-server environment, the sheer amount of 3D data, which can exceed 10 GB, makes it impractical to replicate and transmit data to each individual user. The complexity and performance requirements of rendering applications may also limit the installation of rendering tools on end-users' machines. In this case, a user may send a request to render a dataset stored on a remotely located rendering service that has been specifically designed to handle the complexity and performance requirements of volume visualization. In such client-server environments, the server renders a sequence of 2D images from volumetric data in response to client requests, and then sends those rendered images, through a communication network, to the requesting client. The client will present those images to the user as a stream of images that correspond to the visualization requests of the user.
The quality of service of the remote visualization requires low latency. Often, a near zero wait time at the client side is critical for an efficient clinical workflow. For real-time interactions between users and rendered images, both the rendering and the transmission though a communications network to the client should preferably be fast. Interactive applications prefer not only high-performance rendering by the server, but also prompt transmission through the network. When the communications network is unable to fulfill the bandwidth demand, for example, due to resource limitations and network traffic, compression techniques can be employed to mitigate the bandwidth demand.
In video compression, interframe redundancy, i.e., information common to each frame in a series of frames, is often important for effective compression. In particular, many compression techniques exploit redundancy between neighboring frames, especially when the sampling frequency is high.
Interactive visualization applications, however, have requirements and characteristics that differ from most other visualization applications. Because of these differences, a client may not have sufficient computational power to apply standard video compression methods. Therefore, interactive visualization applications require compression structures, methods, and systems that differ from the existing video compression techniques.